When we’re caring for the plants in our landscape, it works out better if we realize they are capable of responding to threats in their environment.

When I first studied botany some years ago, the prevailing view at that time was that plants were very passive, totally incapable of responding to other organisms in their habitat. In recent years, research has shown just how faulty our limited view of plants really was.

Though plants can’t communicate in the sense of using words, they can use chemical signals and scents that let nearby plants know they are under attack. Of course, they don’t literally scream when diseases or insects attack them. However, the chemicals they release after such onslaughts do put other plants on alert. As a result of this communication, the neighboring plants then release their own chemicals to counter attacks by the same insects and diseases.

As an example, a tobacco plant with tobacco mosaic, a disease, releases a gaseous signal to surrounding plants by converting salicylic acid to oil of wintergreen. The nearby healthy plants then absorb the gas, and use it to boost their own levels of salicylic acid as a defense mechanism against the virus.

Studies at Rutgers University found other plants with similar defense mechanisms. These included sage when it was attacked by insects and tomato plants. After being attacked, the latter undergo chemical changes that make them unpalatable to the insects.

What is even more interesting is that the chemical distress signals sent out by some plants can actually encourage beneficial insects that come to their aid. Plants sending these SOS signals include cotton, tobacco, and corn. The chemical signal attracts specific parasitic wasp species, which then attack the caterpillars feeding on the plants. Corn earworms and tobacco budworms are then wiped out by the wasps. This chemical SOS is released when the caterpillar’s saliva interacts with the damaged leaf tissue.

The plants can release blends of a dozen or more chemical compounds, called volatiles. In tests, the plants actually released plumes of aromatic vapors into the air, which attracted the attention of the helpful wasps. The plants can even release different combinations and concentrations of the gases to attract the appropriate wasp species. That is because parasitic wasps must have very specific caterpillar species to parasitize.

Plants use volatile compounds to kill and repel insects, attract pollinators, and warn other plants of attack.

If plants can “scream,” what other strange things can they do? Scientists did find some edible mushrooms are capable of capturing and using microscopic animals as sources of nutrients. Research at a university in Canada found worms could be paralyzed by a toxin released by the mushroom. Then, the mushroom grew threadlike shoots into the worms, which become a source of nutrient. Scientists in Germany discovered a carnivorous plant, Genisea, preys on protozoa. The plant’s root tips release chemical lures to attract the protozoa. This report was published in Nature.

Sometimes, the chemical compounds produced by plants aren’t always desirable. Some of these can make plants toxic to humans.